SELECT 
  cscart_products.* 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (342, 341, 340, 339, 338)

Query time 0.00025

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_products",
          "access_type": "range",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["product_id"],
          "rows": 5,
          "filtered": 100,
          "index_condition": "cscart_products.product_id in (342,341,340,339,338)"
        }
      }
    ]
  }
}